Dishwasher water level control system



Dec. 19, 1967 J. A. FAY 3,358,703

DISHWASHER WATER LEVEL CONTROL SYSTEM Filed Jan. 14, 1966 FIG. 1.

wwsuroe JOHN A. l-Tay 8) M5 ATTORNEYS HARE/5, K/Ech', RussELL '6: KERN United States Patent 3,358,701 DISHWASHER WATER LEVEL CONTROL SYSTEM John A. Fay, North Hollywood, Calif., assignor to Waste King Corporation, Los Angeles, Calif., a corporation of California Filed Jan. 14, 1966, Ser. No. 520,65 4 Claims. (Cl. 134-57) The present invention relates in general to an automatic dishwasher, Le, a dishwasher having a timercontrolled operating cycle, and, more particularly, to an automatic dishwasher having an improved water level control system which permits the introduction of water into the tub of the dishwasher only when the static water level is below a predetermined maximum and the timer calls for the introduction of water.

The invention contemplates an electrical resistance heating element in the tub adjacent the bottom thereof and below the static water level in the tub when it contains water for washing and rinsing dishes therein, and a primary object of the invention is to provide a water level control system which permits the introduction of water into the tub, when called for by the timer, only when the heating element is exposed to air in the tub, the introduction of water being prevented when the heating element is submerged in water.

More particularly, the invention contemplates a heating element having a high temperature coefiicient of resistance providing it with a low resistance permitting a high current flow therethrough when it operates at a low temperature, and providing it with a high resistance permitting only a low current flow therethrough when it operates at a high temperature. Consequently, the heating element has a low resistance when it is submerged in water in the tub to permit a high current flow therethrough, thereby providing the heating element with a high heat output. Conversely, the heating element has a high resistance when it is exposed to air in the tub, thereby permitting only a low current flow through the heating element and providing it with a low heat output. Such a heating element is self regulating in the sense that its heat output is at a maximum when the tub contains water during washing and rinsing, and is at a minimum when it is exposed to air in the tub during drying of the dishes, thereby preventing overheating during drying. This self regulation of a dishwasher heating element is disclosed and claimed in my Patent No. 3,207,164, issued Sept. 21, 1965.

An important object of the invent-ion is to provide a water level control means responsive to the current flowing through the heating element for permitting the introduction of water into the tub when the heating element is exposed to air in the tub and has a low current flow therethrough, if the introduction of water is called for by the timer, and for preventing the introduction of water into the tub when the heating element is submerged in water and has a high current flow therethrough, even if the introduction of water is called for by the timer under such conditions.

Another object of the invention is to provide a water level control means or system which includes electrically Operated fill valve means for introducing water into the tub, normally closed switch means in series with the fill valve means, and current responsive means in series with the heating element and responsive to the current flowing therethrough for opening the switch means when the heat-ing element is submerged in water in the tub and has a high current fiow therethrough, thereby preventing opening of the fill valve means. Conversely, when the heating element is exposed to air in the tub and has a low current flow therethrough, the current responsive means permits the switch means to remain closed to condition the fill valve means for opening when called for by the timer, which is another object of the invention.

A further object is to provide a dishwasher of the foregoing nature wherein the timer includes normally open switch means in series with the fill valve means and the normally closed switch means, and in parallel with the heating element and the current responsive means, and includes means for closing the normally open switch means when the introduction of water into the tub is required for washing or rinsing dishes therein.

The foregoing objects, advantages, features and results of the present invention, together with various other objects, advantages, features and results thereof which will be evident to those skilled in the dishwasher art in the light of this disclosure, may be achieved with the exemplary embodiment of the invention described in detail hereinafter and illustrated in the accompanying drawing, in which:

FIG. 1 is a side elevational view of a front loading dishwasher which embodies the invention; and

FIG. 2 is a highly simplified, fragmentary, diagrammatic view illustrating the heater and water-level-control circuitry of the invention.

Referring to the drawing, the dishwasher of the invention is designated generally by the numeral 10 and is shown for purposes of illustration as including a tub 12 provided with a downwardly-opening front door 14. Dishes to be washed, rinsed and dried in the tub 12 are adapted to be supported therein by racks 16 and 18 accessible upon opening the door 14. It will be understood, of course, that the invention is not limited to the particular front loading dishwasher 10 shown.

During the main Washing and rinsing operations of the operating cycle of the dishwasher 10, and during any prerinsing operation which may be carried out prior to the main washing operation, water is drawn from the bottom of the tub 12 by a motor-pump assembly 20 and is delivered to a water distributing impeller 22 which sprays the water upwardly over dishes in the racks 16 and 18.

Disposed in the bottom of the tub 12 just below the maximum static water level 24 therein is an electrical heating means 26 for heating the water used for at least the main washing and rinsing operations. Water is introduced into the tub 12 by an electrically operated fill vlave means 28, FIG. 2. The dishwasher 10 also includes a timer or timer means 30, FIG. 2, for controlling the operating cycle of the dishwasher. The heating means 26, the fill valve means 28 and the timer 30 will be described in more detail hereinafter.

The structure of the dishwasher 10 has been illustrated and described in a general way only merely to outline the environmental setting of the invention. It will be understood that the dishwasher 10 includes other components, preferably electrically operated, for performing such functions as draining the water from the tub 12 after each washing or rinsing operation, for circulating heated air over dishes in the racks 16 and 18 during the drying operation, and the like. These operations are carried out under the control of the timer 30'.

Considering the heating means 26 in more detail, it is suitably mounted within a sump 32 at the bottom of the tub 1-2, from which sump water is drawn by the motorpump combination 20 when it is in operation. As hereinbefore pointed out, the heating means 26 is just below the maximum static water level in the tub 12.

T he heating means 26 includes a sheath '34 containing electrical insulating material in which is embedded a resistance heating element 3 6 having a high temperature coefiicient of resistance. For example, this coefiicient may be suliiciently high to increase the current flow through the heating element 36 from the order of four amperes, when the heating means 26 is exposed to air, to of the order of seven amperes when the heating means is submerged in water in the sump 32 at a temperature of the order of 120 F. These current values, it will be understood, are illustrative only and may be varied.

The foregoing increase in current flow through the heating element 36 upon submerging the heating means 26 in water is utilized to open the circuit to the fill valve means 23, thereby eliminating any possibility of overflowing. The manner in which this is accomplished will now be considered in connection with FIG. 2 of the drawing.

Referring thereto, the heating element 36 is shown as connected in series with a current sensitive relay 40 across main power leads 42. More particularly, the relay 40 includes a normally closed switch or switch means 44 in series with the fill valve means 28 and in parallel with the heating element 36. The relay 40 also includes an electromagnet 46 capable of opening the switch 44 when the current flow through the heating element 36 reaches a valve approaching the maximum. For example, the electromagnet 46 may open the switch 44 when the current flow through the heating element 36 reaches six amperes, under the conditions wherein the current flow is four amperes when the heating element is exposed to air and seven amperes when it is submerged in water.

The -fill valve means 28 is shown as including a valve 48 operable by an electromagnet 50 when the latter is energized, this electromagnet being connected in series with the normally closed switch 44 and in parallel with the heating element '36 and the electromagnet 46. The valve 48 is connected to a suitable source of water and discharges into the tub 12 in a conventional manner, not shown.

The timer 30 includes a timer motor 52 connected in parallel with the heating element 36 and electromagnet 46 and in parallel with the normally closed switch 44 and electromagnet 50. As is conventional, the timer motor 52 drives suitable cams, not shown, one of which closes a normally open switch or switch means 54 whenever water is to be introduced into the tub 12. The switch 54 is connected in series with the normally closed switch 44 and the electromagnet 50, and in parallel with the heating element '36 and the electromagnet 46.

The circuit may also include a manual, start switch 56 controlling all of the elements in the circuit.

Operation Initially, it will be assumed that there is no water in the sump 32 -and that the main switch 56 is closed, thereby energizing the timer motor 52 and the heating element 36. It will also be assumed that the timer motor 52 has not yet closed the switch 54. Under such conditions, the heating element 36 operates at a high temperature providing it with a high resistance so that the current flow through the electromagnet 46 is insufiicient to open the normally closed switch 44.

If the timer motor 52 now closes the switch 54 to introduce water into the tub 12 for washing or rinsing purposes, the circuit through the electromagnet "50 controlling the fill valve 48 is completed to open the fill valve. Upon opening of the fill valve, the water level in the sump 32 rises until the water contacts the heating means 26. The water then begins to reduce the temperature of the heating element 36 to reduce its resistance and increase the current flow therethrou-gh. By the time the water level reaches the maximum static level 24, thereby completely submerging the heating means 26, the temperature of the heating element 36 is reduced enough to cause the current flow therethrough to reach a value sulficient to energize the electromagnet 46 and open the switch 44. Opening of the latter switch results in de-energization of the electromagnet 50, and closure of the fill valve 48,

4 even if the timer motor 52 has not yet opened the switch 54.

It will be noted that the foregoing discussion implies a slight time lag in the current response of the heating element '36. This slight time lag is due to the fact that a little time is required to dissipate heat from the heating element 36 through the electrical insulating material between it and the sheath 34. Consequently, the fill valve circuit is not opened when water first comes in contact with the heating means 26, there being a slight time lag sufiicient only to permit the water level to rise to the desired maximum static level 24, wherein the heating means 26 is just submerged, before the heating element 36 cools enough to cause the electromagnet 46 to open the switch 44. Preferably, the time lag is sufficient only to permit the water level to rise above the heating means 26 a distance of the order of one-sixteenth inch or so, thereby providing accurate water level control.

As will be apparent from the foregoing, the present invention positively precludes any possibility of overflow of the sump 32 since the fill valve 48 cannot be opened to introduce water into the tub 12 as long as the heating element 36 has been submerged in water a sufficient length of time to open the switch 44. Conversely, water can be introduced into the tub 12 only after the heating element 36 has operated in air long enough for the current flow therethrough to be reduced to a value sufficiently low that the electromagnet 46 permits the switch 44 to close.

Thus, the present invention provides a very simple overflow-preventing control system which merely relies on the difference between the electrical currents flowing through the heating element 36 when it is submerged in water and when it is exposed to air, which is an important feature of the invention.

Although an exemplary embodiment of the invention has been disclosed herein for purposes of illustration, it will be understood that various changes, modifications and substitutions may be incorporated in such embodiment without departing from the spirit of the invention as defined by the claims which follow:

1. In a dishwasher, the combination of:

(a) a tub adapted to contain dishes to be washed and rinsed and adapted to contain water for washing and rinsing them;

(b) an electrical resistance heating element in said tub adjacent the bottom thereof and below the static water level in said tub when it contains water for washing and rising dishes therein;

(c) said heating element having a high temperature coeflicient of resistance providing it with a low resistance permitting a high current flow therethrough when it operates at a low temperature, and providing it with a high resistance permitting only a low current flow therethrough when it operates at a high temperature;

(d) whereby said heating element has a low resistance and a high current flow therethrough when it is submerged in water in said tub and has a high resistance and a low current flow therethrough when it is exposed to air in said tub; and

(e) control means responsive to the current flowing through said heating element for permitting the introduction of water into said tub when said heating element is exposed to air in said tub and has a low current flow therethrough, and for preventing the introduction of water into said tub when said heating element is submerged in water in said tub and has a high cur-rent flow therethrough.

2. A dishwasher according to claim 1 wherein said control means includes:

(a) fill valve means for introducing water into said tub; and

(b) means responsive to the current flowing through said heating element for permitting opening of said fill valve means when said heating element is ex- 5 6 posed to air in said tub and has a low current flow 4. A dishwasher according to claim 3 including a timer therethrough, and for preventing opening of said fill comprising: valve means when said heating element is submerged (a) normally open switch means in series with said fill in water in said tub and a has a high current flow valve means and said normally closed switch means, therethrough. 5 and in parallel with said heating element and said 3. A dishwasher according to claim 1 wherein said concurrent responsive means; and trol means includes: (b) means for closing said normally open switch (a) electrically operated fill valve means for intromeans.

ducing Water into said tub; (b) normally closed switch means in series with said 1 References Cited i 1 valvetmeans; n h t 0 UNITED STATES PATENTS c curren responsive means in series w1 sai ea 2,781,765 2/1957 Steidley 13457 mg element and responsive to the current flowing 3,207,164 9/1965 Fay 134 57 therethrough, and in parallel with said fill valve means and Sam twltch P f 15 CHARLES A. WILLMUTH, Primary Examiner. means when said heating element 1s submerged 1n water in said tub and has a high current flow there BLEUTGE, Examinerthrough. 

1. IN A DISHWASHER, THE COMBINATION OF: (A) A TUB ADAPTED TO CONTAIN DISHES TO BE WASHED AND RINSED AND ADAPTED TO CONTAIN WATER FOR WASHING AND RINSING THEM; (B) AN ELECTRICAL RESISTANCE HEATING ELEMENT IN SAID TUB ADJACENT THE BOTTOM THEREOF AND BELOW THE STATIC WATER LEVEL IN SAID TUB WHEN IT CONTAINS WATER FOR WASHING AND RISING DISHES THEREIN; (C) SAID HEATING ELEMENT HAVING A HIGH TEMPERATURE COEFFICIENT OF RESISTANCE PROVIDING IT WITH A LOW RESISTANCE PERMITTING A HIGH CURRENT FLOW THERETHROUGH WHEN IT OPERATES AT A LOW TEMPERATURE, AND PROVIDING IT WITH A HIGH RESISTANCE PERMITTING ONLY A LOW CURRENT FLOW THERETHROUGH WHEN IT OPERATES AT A HIGH TEMPERATURE; (D) WHEREBY SAID HEATING ELEMENT HAS A LOW RESISTANCE AND A HIGH CURRENT FLOW THERETHROUGH WHEN IT IS SUBMERGED IN WATER IN SAID TUB AND HAS A HIGH RESISTANCE AND A LOW CURRENT FLOW THERETHROUGH WHEN IT IS EXPOSED TO AIR IN SAID TUBE; AND (E) CONTROL MEANS RESPONSIVE TO THE CURRENT FLOWING THROUGH SAID HEATING ELEMENT FOR PERMITTING THE INTRODUCTION OF WATER INTO SAID TUB WHEN SAID HEATING ELEMENT IS EXPOSED TO AIR IN SAID TUB AND HAS A LOW CURRENT FLOW THERETHROUGH, AND FOR PREVENTING THE INTRODUCTION OF WATER INTO SAID TUB WHEN SAID HEATING ELEMENT IS SUBMERGED IN WATER IN SAID TUB AND HAS A HIGH CURRENT FLOW THERETHROUGH. 